1. Field of the Invention
The present application relates to a mother substrate for a liquid crystal display device and a method of fabricating the mother substrate, and more particularly, to a mother substrate including an electrostatic discharge pattern and a method of fabricating a liquid crystal display device using the mother substrate.
2. Discussion of the Related Art
In general, liquid crystal display (LCD) devices use the optical anisotropy and polarization properties of liquid crystal molecules of a liquid crystal layer to produce an image. The liquid crystal molecules have long and thin shapes. Because of the optical anisotropy property, the polarization of light varies with the alignment direction of the liquid crystal molecules. The alignment direction of the liquid crystal molecules can be controlled by varying the intensity of an electric field applied to the liquid crystal layer. Accordingly, a typical LCD device includes two substrates spaced apart and facing each other and a liquid crystal layer interposed between the two substrates. Each of the two substrates includes an electrode on a surface facing the other of the two substrates. A voltage is applied to each electrode to induce an electric field between the electrodes. The arrangement of the liquid crystal molecules as well as the transmittance of light through the liquid crystal layer is controlled by varying the intensity of the electric field. LCD devices are non-emissive type display devices that employ a light source to display images using the change in light transmittance.
Among the various types of LCD devices, active matrix LCD (AM-LCD) devices that employ switching elements and pixel electrodes arranged in a matrix structure are the subject of significant research and development because of their high resolution and superior suitability for displaying moving images.
FIG. 1 is a perspective view of a liquid crystal display device according to the related art. As shown in FIG. 1, the liquid crystal display (LCD) device of the related art includes a first substrate 10, a second substrate 20 and a liquid crystal layer 30. The first substrate 10, which is referred to as an array substrate, includes a gate line 14 and a data line 16 crossing each other to define a pixel region P. A pixel electrode 18 and a thin film transistor (TFT) Tr, as a switching element, are positioned in each pixel region P. The TFT Tr, which is disposed adjacent to crossings of the gate lines 14 and the data lines 16, is disposed in a matrix on the first substrate 10. The second substrate 20, which is referred to as a color filter substrate, includes color filter layer 26 including red (R), green (G) and blue (B) color filters 26a, 26b and 26c, a black matrix 25 between the red, green and blue color filters 26a, 26b and 26c and a common electrode 28 on both the color filter layer 26 and the black matrix 25.
Although not shown in FIG. 1, the first and second substrates 10 and 20 are attached with a seal pattern to prevent leakage of liquid crystal layer 30. In addition, a first alignment layer is formed between the first substrate 10 and the liquid crystal layer 30 and a second alignment layer is formed between the second substrate 20 and the liquid crystal layer 30 to align the liquid crystal molecules in the liquid crystal layer 30 along an initial alignment direction. A polarization plate is formed on an outer surface of at least one of the first and second substrates 10 and 20.
Further, a backlight unit (not shown) disposed under the first substrate 10 supplies light. A gate signal turning the TFT Tr on is sequentially applied to each of the gate lines 14, and an image signal on the data line 16 is applied to the pixel electrode 18 in the pixel region P. The liquid crystal molecules in the liquid crystal layer 30 are driven by a vertical electric field generated between the pixel electrode 18 and the common electrode 28 to display images by varying the light transmittance of the liquid crystal molecules.
The LCD device is completed through an array substrate process, a color filter substrate process and a cell process. The pixel electrode 11 and the TFT Tr are formed on each pixel region P of the first substrate 10 in the array substrate process, and the color filter layer 26, the black matrix 25 and the common electrode 28 are formed on the second substrate 20 in the color filter substrate process. Further, the first and second substrates 10 and 20 are attached and liquid crystal molecules are injected between the first and second substrates 10 and 20 in the cell process.
To improve productivity, a plurality of array substrates are obtained by forming a plurality of unit array patterns on a single mother substrate and cutting the single mother substrate. Similarly, a plurality of color filter substrates are obtained by forming a plurality of unit color filter patterns on a single mother substrate and cutting the single mother substrate. As a result, a plurality of LCD devices are obtained from two mother substrates by attaching the plurality of array substrates and the plurality of color filter substrates.
FIG. 2 is a plane view showing a mother substrate according to the related art, and FIG. 3 is a cross-sectional view taken along a line of FIG. 2.
In FIG. 2, a plurality of unit array patterns 55 are formed on a mother substrate 50. Although not shown in FIG. 2, a gate line, a data line, a thin film transistor (TFT) and a pixel electrode are formed in an inner portion of each unit array pattern 55. The gate line and the data line cross each other to define a pixel region and the TFT as a switching element is connected to the gate line and the data line. The pixel electrode is connected to the TFT.
In addition, a metal pattern 60 having a closed rectangular loop shape and surrounding the plurality of unit array patterns 55 is formed in an edge portion of the mother substrate 50. The metal pattern 60 has the same layer and the same material as the gate line such that the metal pattern 60 is formed directly on the mother substrate 50. Subsequently, a plurality of layers such as a gate insulating layer 70, a semiconductor layer (not shown) and a passivation layer 80 are formed on the metal pattern 60 in a vacuum apparatus (not shown).
The metal pattern 60 is used for preventing static electricity generated at an outer portion thereof. When static electricity having a relatively high voltage is generated at the mother substrate 50, the static electricity is transmitted along a conductive line and is discharged at an electrically weak portion. For example, the static electricity may be discharged as a spark at the electrically weak portion and the electrically weak portion may be broken. In the absence of the metal pattern 60, the static electricity may be concentrated on elements of each unit array pattern 55, for example, the TFT, and the elements may be broken. However, since the static electricity generated at the outer portion of the metal pattern 60 is transmitted along the metal pattern 60 and does not penetrate into the inner portion of the metal pattern 60, the elements of each unit array pattern 55 are protected from the static electricity. As a result, while the plurality of layers are deposited in the vacuum apparatus, the metal pattern 60 prevents static electricity generated in a corner portion of the mother substrate 50 from penetrating into the plurality of unit array patterns 55.
However, the metal pattern 60 does not remove static electricity generated at the inner portion of the metal pattern 60. During a process of the mother substrate 50 in the vacuum apparatus, although most of the static electricity is generated at the corner portion of the mother substrate 50, some of the static electricity is generated at a central portion of the mother substrate 50. In addition, when the mother substrate 50 is loaded on and unloaded from a stage of an apparatus, e.g., a measurement apparatus, an inspection apparatus or an exposure apparatus, different from the vacuum apparatus, the static electricity is generated at a random portion of the mother substrate 50. As a result, the plurality of unit array patterns 55 may be deteriorated by the static electricity generated at the inner portion of the metal pattern 60 even when the metal pattern 60 is formed on the mother substrate 50.
The mother substrate 50 is cut into a plurality of array substrates each including the unit array patterns 55. Similarly, the other mother substrate (not shown) is cut into a plurality of color filter substrates. Each array substrate and each color filter substrate are attached to form an LCD device, and inspection is performed for the LCD device. When the LCD device is judged to be deteriorated, the LCD device is renounced. As a result, a good color filter substrate attached to a bad array substrate is renounced, and production cost increases.
To reduce the production cost, inspection may be performed before the mother substrate is cut. After the mother substrate is cut, the array substrate judged to be deteriorated is renounced, and the array substrate judged to be not deteriorated and the color filter substrate are attached to form an LCD device. Accordingly, production cost may be partially reduced. However, since the number of steps for injecting liquid crystal materials and attaching the array substrate and the color filter substrate increase, productivity is reduced and fabrication time increases.